<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>4-超时与取消请求</title>
  </head>
  <body>
    <button>发送请求</button>
    <button>取消请求</button>

    <script>
      const buttons = document.querySelectorAll('button')

      let xhr
      buttons[0].onclick = () => {
        xhr = new XMLHttpRequest()
        xhr.open('GET', 'http://localhost:8081/delay-server')


        // 指定超时时间  应用中一般会指定为20--30s
        xhr.timeout = 20000 // ms为单位
        // 专门监视超时错误
        xhr.ontimeout = () => {
          alert('超时错误!')
        }

        xhr.onreadystatechange = () => {
          console.log(xhr.readyState, xhr.status, xhr.responseText)
          if (xhr.readyState===4) {
            console.log('-----', xhr.status, xhr.responseText)
          } 
        }
        xhr.send()
        
      }

      buttons[1].onclick = () => {
        // 中断请求
        xhr.abort()
        console.log('中断请求')
      }
    </script>
  </body>
</html>
